Generally, a secondary battery may be recharged and manufactured as a large capacity battery. As a representative secondary battery, there may be a nickel cadmium battery, a nickel hydrogen battery, a lithium ion battery, and the like. Among them, the lithium ion battery is receiving attention as the next generation power source due to excellent characteristics thereof, such as, long lifespan and high capacity. Here, the operation voltage of the lithium secondary battery is 3.6V or higher. The lithium secondary battery is used as a power supply of a mobile electronic device or several lithium secondary batteries are connected in series, to thereby be used in a high-powered hybrid vehicle. The use of the lithium secondary battery is rapidly increasing since the operation voltage of the lithium secondary battery is three times higher than that of the nickel-cadmium battery or the nickel-metal hydride battery and energy density characteristics per unit weight of the lithium secondary battery is excellent.
The lithium secondary battery may be manufactured in various types, and the representative type thereof may be a cylinder type and a prismatic type that are mainly used in the lithium ion battery. A lithium polymer battery that has been spotlighted recently is manufactured in a flexible pouched type, and thus, the shape thereof is relatively free. In addition, the lithium polymer battery has excellent safety and a small weight, and thus is favorable in slimming and weight-lightening of a mobile electronic device.
A battery cell of a secondary battery includes a battery part and a case for providing a space in which the battery part is contained. A battery pack is composed of several battery cells having the foregoing configuration connected in series or in parallel with each other. Here, technology for protecting a case made of a flexible material has been requested.